In the triangle arrangement, the beam of transmitter and receiver is cut off by photoelectric switch at the top corner.
The target object can only be detected within the range of overlapping beams.
If the reflected or diffuse reflected light is not within the limit, it cannot be recorded by the photoelectric switch. In the triangle arrangement, relatively small distance changes (such as the offset of slot and axis) can be identified.
The color and shape of objects have little effect on the recording.